Process for treating mineral oils



`Iuly 14, 1936. w. B. MccLUl-:R T Al.

PROCESS FOR TREATING MINERAL OILS Filed April 18, 1934 Patented july 14., B936 UNITED sTA'rEs 2,047,380 PROCESS FOR TREATING MINERAL OILS Wilbert B. McCluer and Merrell R. Fenske, State College, Pa;, assignors to Pennsylvania Petroleum Research Corporation, a corporation of Pennsylvania Application April 18, 1934, Serial No. 721,212 1s claims. (c1. '19e-1s) This invention pertains generally to the separation of mineral oils into components. It will be described in connection with the improvement of lubricating stocks of Pennsylvania grade.

5 However, it is to be understood that it may have other uses.

In accordance with this invention crude petroleum or products thereof and particularly lubricating oils are separated into various components by treatment with methyl salicylate or a mixture containing methyl salicylate in sufcient quantity to be effective as such.

While we appreciate that practically nothing is known concerning definite substances which comprise the complicated mixture known as mineral oil and still less is known concerning the cornpounds present in the heavier or lubricating oil fractions except that the molecular weights of o the molecules are large, which makes it possible to have varying types of structure existing in the same molecule, yet there is evidence which leads to the conception that the types of molecules in lubricating oils may be divided into perhaps three classes.

The molecules of these three classes are thought to have structures containing rings and chains and the following hypothetical classification is based, iirst, upon whether the rings are v unsaturated or saturated,`and second, upon the relative length of the chains attached to the rings.

The term chain" implies either substantially a straight chain or a relatively highly branched chain.

The molecules of the rst class are conceived to have rings which are appreciably unsaturated (i. e. hydrogen may be added without appreciably changing the molecular conguration) 40 with chains attached to the rings but with the ring type of structure preponderating. Molecules of this class may be regarded as having asphaltic characteristics.

The molecules of the second class are conceived to have rings which are ,principally saturated, such as those of cyclopentane or cyclohexane, with a considerable number of chains attached thereto. The carbon atoms are thought to be about equally divided between the chains and the rings. Molecules of this class may be regarded as having naphthenic characteristics.

The molecules of the third class are conceived to have rings which are predominantly saturated i (i. e. the larger part of the carbon atoms havechains of the second class. The carbon atoms in the chains are thought to be materially in excess of those in the rings. This class of molecules may be regarded as having paraiiinic characteristics.l

It is to be understood, however, that the fore- 5 going thoughts relative to molecular arrangements are employed simply to portray the overall or average condition of the molecular species constituting an oil and that any one or more of such molecular arrangements may comprise pe- 10 troleums or oils according to the type.

Oils of Pennsylvania grade are composed preponderately of molecules of the third class.

Solvent extraction processes of the prior art relate principally to the removal of molecules of the rst and second classes from oils containing considerable quantities of such molecules, such as those from the Mid-Continent and Western fields, the desideratum being the production of ,n railinates which are comparable in viscosity c characteristics to Pennsylvania oils. The improvements obtained in such processes are due principally to deasphaltization, or in other words to the removal of materialsnot initially contained in oils of Pennsylvania grade.

Oils of Pennsylvania grade are universally regarded as premium lubricants and improvements in such oils by the process herein are due to a considerably different effect, and entirely sep- 30 arate and distinct problems are involved.

Outstanding among these problems is the removal from lubricating oils of Pennsylvania grade of materials responsible for the relatively high Conradson carbon residue which is particularly characteristic of these oils. This problem is of equal if not of greater importance than that of decreasing the rate of change of viscosity with temperature. This problem is not of equal importance in thereflning of lubricating oils derived from crudes emanating from oil elds outside of the Pennsylvania area. The absence of a relatively high Conradson carbon is substantially the only characteristic in which lubricating oils derived from crudes outside of the Pennsylvania area may be regarded as being of a quality comparable to Pennsylvania grade lubrieating oils.

The rate of change of viscosity with temperature is at present largely measured in terms of the viscosity index as developed by Dean and Davis (Chemical and Metallurgical Engineering 36,618 (1929) and revised by Davis, Lapeyrouse, and Dean (Oil Gas Journal, 30 (46), 92 (1932)). 55

It is also measured in terms of a relation shown to exist between Saybolt viscosity and gravity for oils of any particularl type (Hill and Coates, Industrial Engineering Chemistry 20,641 (1928)), this relationship being expressed in terms of the 60 viscosity gravity constant calculated from the equation:

10G-1.0752 log 1007-38) 10-log 10(V-38) A=viscositygravity constant G=specic gravity at 60 F. V=viscosity at 100 F., Saybolt seconds oils are regarded as being of low quality and give a value of approximately 0.92.

Since the rate of change in viscosity of oil mixtures with temperature decreases with decrease in percentage of molecules of the first and second classes, it would appear that either the viscosity index or the viscosity-gravity constant is a measure of the viscosity-temperature characteristic of an oil.

However, both methods of measuring the latter characteristic present diiculties.

For instance, the viscosity index, particularly of light oil fractions, is influenced to a great extent by the accuracy with which the 210 F. viscosity is determined, and also, though to a less extent, by the accuracy with which the 100 F.

viscosity is determined.

For example, an error of 1.0 Saybolt second in the 210 F. viscosity determination of a 40.0- second (Saybolt at 210 F.) oil results in an error of approximately 32 points in the viscosity index of a typical parafnic oil, and in an error of about 55 points in the viscosity index of a typical naphthenic oil. A similar error in the case of a 45.0-second (Saybolt at 210 F.) oil results in an error of about 15 points for a parainic oil and in an error of 27 points for a naphthenic oil.

The influence of the accuracy of the 100 F. viscosity determination is about one-tenth of that of the 210 F. viscosity determination.

In the case of heavier oils, the possible error due to inaccurate viscometry methods is somewhat less important but yet must be taken into consideration.

Therefore, it will be seen that very large differences in viscosity index measurements may result owing to relatively small errors in viscosity measurements, particularly in the case of light oil fractions, making it necessary to exercise a very high degree of skill and care to obtain reasonably correct readings.

A difference of a comparable character does not find its way into viscosity-gravity constant determinations in the case of light oil fractions so that the latter method may be regarded as being somewhat more accurate in the case of light oil fractions.

However, viscositygravity constant determinations require a much greater amount of' calculations and this method is, therefore, cumbersome, particularly when investigations are made on a large scale.

Upon an investigation of a representative group of different oils, it is found that a. denite relation exists between the yviscosity index and the viscosity gravity constant making it possible by a combination of the two to evaluate the viscosity-temperature characteristics of an oil by a third and much more uniformly accurate and rapid method than the first and second methods respectively.

This will be more clearly understood upon reference to the drawing in which Figure 1 is a graph on which the viscosity indexes of the above group of oils are plotted against their viscosity gravity constants.

Figure 2 is a graph on which viscosities in Saybolt seconds at 100 F. are plotted against specific gravities at 60 F., the values of each having been obtained by substituting for A in the above formula the numerical value of the viscosity gravity constant (as obtained from the graph of Figure 1) corresponding to each of a. series of hypothetical oils having viscosity indexes ten umts apart and ranging from Zero to 120; and by substituting for V in the above formula a plurality of arbitrarily chosen values; and on which graph a curve is drawn through the platted points resulting from each chosen value of visf This fact indicates and tests have shown that an index number comparable to its viscosity index number (hereinafter referred to for convenience as the gravity index) can be obtained for any mineral oil lubricant of any one type from its viscosity in Saybolt seconds at 100 F. and its specific gravity at 60 F. with a fairly high degree of accuracy.

Furthermore, the nature of curve I0 shows that gravity index numbers may be obtained for Pennsylvania oils (being parafnic in type) with a high degree of precision.

A form of graph from which the gravity index of a mineral lubricating oil can be obtained accurately is shown at I2 in Figure 2. The curves I3, I4, I5, I6, II, I8, I9, 20, 2|, 22, 23, 24 and 25 were constructed by connecting all of the points plotted in the manner above indicated for each hypothetical oil. Curves I4, IS, I8, 20, 22, and 24 are shown dotted merely to assist the eye in focusing on any one line.

It is appreciated that the accuracy of such a graph is dependent to a large extent on its size, but the usual 8.5 by 11 inch plot will result in values which are approximately of the same degree of accuracy as that which corresponds to an error of 0.10 A. P. I. in gravity.

To obtain the numerical value of the gravity index for any mineral oil of the type for which graph I2 happens to be constructed whether such o1l is extracted or not, it is merely necessary to measure its viscosity at 100 F. in Saybolt seconds, to measure its gravity at 60 F., and then to plot the values on graph I2 of Figure 2, interpolating the exact value if necessary. Additional curves may be interpolated between those shown if desired to assist in the reading.

This invention is based on the discovery that the gravity index, color and/or Conradson carbon residue of mineral oils in general and Pennsylvania grade oils in particular may be improved by treating such oils with methyl salicylate. Methyl salicylate (ortho hydroxy methyl benzoate HOCGH4 COOCH3) is found to be particularly effective.

Oil components in general and particularly aoliveo those of Pennsylvania grade possess a selective solubility in solvents of the character above set forth in that those components which are largely responsible for a relatively high viscosity change with temperature, for a relatively dark color and/or for a relatively high Conradson carbon residue are more soluble therein than other oil components not possessing these characteristics. Therefore, by an extraction treatment of an oil containing both classes of components with methyl salicylate, it is possible to separate said oil into an oil having a relatively higher viscosity change with temperature, a relatively darker color and/ or a relatively higher Conradson carbon residue and an oil having a relatively lower viscosity change with temperature, a relatively lighter color and/or a relatively lower Conradson carbon residue than that possessed by the original oil.

Furthermore, the solvents herein set forth exhibit a selective solvent power for oxidizable components and for other components which might result in sludge, and for other substances considered deleterious, so that, when the original oil contains one or more of the foregoing, a preponderance thereof will be found in the separated portion of relatively high viscosity change with temperature, of relatively darker color and/or of relatively higher Conradson residue, thereby leaving the separated portion of relatively low viscosity change with temperature, of relatively lighter color and/or of relatively lower Conradson carbon residue in a highly refined state.

In practicing the invention, contact between solvent and oil may be effected by any desired means. Two immiscible solutions will generally be eventually formed, one containing oil components of relatively higher gravity index, of relatively lighter color and/or of relatively lower Conradson carbon residue, and the other solution containing oil components of relatively lower gravity index, of relatively darker color and/or of relatively higher Conradson carbon residue.

This contact may be the result of mechanically mixing the oil with a suitable quantity of methyl salicylate such as by stirring in a suitable container at any desired suitable temperature to effeet either a total or any desired degree of partial solution of solvent and oil. In the event of total solution of the oil and solvent, the mixing may be followed by cooling to cause the formation of two immiscible solutions the same as when partial solution only of oil in solvent is originally elected. This cooling may be in steps so as to cause fractional precipitation. It is also possible to effect r partial solution of oil in solvent at a relatively elevated temperature and then to cool to precipitate a part of the dissolved oil.

Separation of the solutions may be accomplished in any manner, for instance, by allowing the liquid to settle into a two layer system and then decanting, or by centrifuging the liquid.

The solvent may be removed from each of the separated solutions by any suitable means, for instance, by distillation.

The extraction may be repeated on either separated oil portion as many times as desired either with or without the previous separation of solvent therefrom. For instance, the solvent would be separated `from the oil portion if it should be desired to treat such portion with a different solvent without effecting a mixture of said solvents. However, such separation except as indicated would generally be unnecessary.

l The oil might also be treated in a batch countercurrent system wherein the solvent in batches moves countercurrently through a plurality of oil batches, each batch of solvent being separated from each batch of oil before moving on to the However, any type of apparatus or system may be employed without departing from the invention.

The following examples will serve to further illustrate the invention. Properties of Pennsylvania lubricating stocks used Oil Bright Cylinder stock stock Viscosity at 210 F 153 154. 4 Viscosity at F 2517 2370 Gravity, A. P. I 25.9 25.9 Flash point. F 550 565 Fire point. "F 620 635 Pour point, F 15 50 Per cent Conradson carbon 1. 728 2. 178 Color (A. S. T. M. and/or cms.) 8 23. 6-D Viscosity index 97. 0 102, 0 Viscosity gravity constant 0. 809 0. 810 106 105 Gravity index the column relate to the properties of the extract.

Extraction of bright stock Run No Solvent-oil vol. ratio. Extraction temp. F Yield of raflinate. Yield of extract Viscosity at 210 F Viscosity at 100 F Gravity, A. P. I Flash point, "F Fire point, F Pour point. F. Percent Conradson carbon Color (A. S. T. M. and/or cms.) Viscosity index Viscosity-gravity constant Gravity index The following runs were made with methyl salicylate as the solvent and cylinder stock as the oil.

left and becoming less extreme at the right, but there is, nevertheless, a decided downward tend- Ecctractz'on of cylinder stock Run No 7B. 8B. 8E QR 10R 11R 12R Solvent-oil vol. ratio 1 5:1 2:1 6:1 2:1 6.5:1 12:1 Extraction temp. F 77 77 77 32 32 32 Yield of raffinate. 55 54 17 76 58 42 Yield of extract 45 46 83 24 42 58 Viscosity at 210 F 153. 2 146. 1 150. 2 163. 4 Viscosity at 130 F 852 8 2 804 780 840 Viscosity at 100 F 2175* Am25* 1930' 2030 Gravityr A. P. I... 26. 7 27. 2 28.3 @.8 Pour point, F

Percent Conradson carbon 1. 744 Color (A. S. T. M, and/or cms.) 38.5-D 43.0-D 45.4-D 36.6-D 38.3-D Viscosity index 106. 0 108 73. 5 113 106 111 114 Viscosity-gravity constant. 0.805 0.802 0. 822 0.787 0. S01 0. 794 0. 788 Gravity index 109 111 97 118 111 115 118 Note: Asterisks denote extrapolated viscosites.

In all of the foregoing runs, contact between solvent and oil was made by single batch methods. Greater efiiciencies may be obtained by employing more eicient methods, for instance, continuous countercurrent.

While any desired temperature maybe employed in carrying out the process, for the extraction of neutral or similar light oils, or oils containing substantial quantities of light constituents a temperature substantially below 32 F. is recommended, particularly if the degree oi miscibility of the oil and solvent is too high for eicient layer formation. Or a substance or substances might be added to the solvent to reduce.

or otherwise modify the solubility of hydrocarbons therein. This may also apply in the case'of heavier oils, if desired.

In the foregoing data with respect to color the smaller numerals show the color as measured by A. S. T. M. methods.

The larger numerals, which are referred to as indicating centimeters, show a` relative relationship with 100 centimeters indicating the color of a water-white oil and 0 centimeters an oil suirlciently opaque to cut down the quantity of light transmitted with the light source 0 centimeters away to the same quantity as would pass through the water-white oil with the light source 100 centimeters away.

An increase in centimeters, therefore, indicates improvement in color.

In some cases the products obtained were too dark for determination on this specially constructed colorimeter in the usual manner. In this case. the oils were diluted with kerosene. The kerosene used for dilution had a color rating of centimeters. Accordingly all colors reported for these darker products were obtained on kerosene-oil mixtures containing 85% by volume kerosene and 15% by volume oil. The readings so obtained are listed with the suix D.

The degree of actual improvement in the above runs will be better appreciated upon examining Figure 3 wherein is shown a graph 26 having curves 21, 28, 29, 30, 3l, 32 and 33. Curve 21 was constructed by plotting the viscosity indexes of a series of hypothetical oils against their viscosities in Saybolt seconds at 210 F. Each of the series of hypothetical oils was assumed to have no viscosity dilerence between F. and 210 F. The curve 21, therefore, represents maximum improvement as far as the viscosity-temperature characteristic of an oil is concerned.

It will be noted that the curve 21 slopes down- Wardly toward the right, the slopes at the various points on the curve 21 being. quite extreme at the ency. This is due to the manner in which the viscosity index was originally developed and clearly shows that a diierence of one point in the viscosity index of an oil of, for instance, 280 seconds viscosity at 210 F. is of as much importance as a difference of about 3.5 points in the viscosity index of an oil having a viscosity of, for instance, 40 seconds at 210 F.

The curves 21 to 33 inclusive have been interpolated to represent diierent percentages of imu provement in viscosity index over that normally possessed by a Pennsylvania grade oil. Base line 34 is given a. value of 100 since Pennsylvania. oils are rated at 100 in viscosity index. Curve 33 represents an improvement of 10%; curve 32, 20%; curve 3|, 30%; curve 30, 40%; curve 29, 60%; and curve 28, 80%.

From the foregoing it will be seen that a. mineral oil and particularly one of Pennsylvania grade may be divided into any desired number of portions having different gravity indexes, having diierent color rating and/or having different Conradson carbon residue ratings and may be simultaneously otherwise refined.

Since it is much more difllcult to improve a petroleum oil' of Pennsylvania. grade due to its original high quality and since such oils may be very substantially improved by the process herein, it follows that the process will eiect very substantial improvements in other oils such as those of naphthenic and/or asphaltic characteristics.

In the claims, the term lubricating oil when referred to is intended to mean an oil of a viscous character, that is, of the order of 40 Saybolt seconds at 210 F. or above.

Also in the claims the term lubricating oil residuum of Pennsylvania grade is intended to means a residuum resulting from the distillation of Pennsylvania grade crude oil or of a relatively heavy fraction thereof, or a Pennsylvania grade oil of comparable viscosity obtained by any other means, and is employed generically to include a mixture of such residuums, or a mixture containing a quantity of such residuum. These oils will have viscosities at 210 F. above 100 Saybolt seconds and usually a viscosity at 210 F. in the neighborhood of Saybolt seconds or above.

While procedure for the purpose of carrying out the invention has been particularly described, it is to be understood that this is by way of illustration, and that changes, omissions, additions, substitutions, and/or modifications may be made without departing from the spirit of the invention which is intended to be limited only as required by the prior art.

exhibiting certain of said characteristics to a greater and to a lesser degree.

2. A process comprising extracting a mineral oil containing components of different gravity index with methyl salicylate under conditions adapted to cause the formation of two liquid phases to produce portions of said oil respectively of higher and lower gravity index.

3. A process comprising extracting a mineral oil containing components of different color with methyl salicylate under conditions adapted to cause the formation of two liquid phases to produce portions of said oil respectively of lighter and darker color.

4. A process comprising extracting a mineral oil containing components responsible for Conradson carbon residue with methyl salicylate under conditions adapted to cause the formation of two liquid phases to produce portions of said oil respectively of higher and lower concentrations of said components.

5. A process comprising extracting a petroleum oil of Pennsylvania grade containing components of different characteristics with methyl salicylate under conditions adapted to cause the formation of two liquid phases to produce portions of said oil respectively exhibiting certain of said characteristics to a greater and to a lesser degree.

6. A process comprising extracting a petroleum oil of Pennsylvania grade containing components of different gravity index with methyl salicylate under conditions adapted to cause the formation of two liquid phases to produce portions of said oil respectively of higher and lower gravity index.

`'1. A process comprising extracting a petroleum oil of Pennsylvania grade containing components of different color with methyl salicylate under l conditions adapted to cause the formation of two liquid phases to produce portions of said oil respectively of lighter and darker color.

8. A process comprising extracting a petroleum oil of Pennsylvania grade containing components responsible for Conradson carbon residue with formation of two liquid phases to produce portions of said oil respectively of higher and lower concentrations in components responsible for Conradson carbon residue.

11. A process comprising contacting a petro- 5 leum oil with methyl salicylate under conditions conducive to the formation of two liquid phases, and separating said phases to produce oil portions of higher and lower` gravity index.

12. A process comprising contacting a petro- 10 leum oil with methyl salicylate under conditions conducive to the formation of two liquid phases, and separating said phases to produce oil portions of higher and lower gravity index, said petroleum oil being o1" a character such that the 15 raffinate portion will have a viscosity index above 100.

13. A process comprising contacting a lubricating oil of Pennsylvania grade containing components of different characteristics with methyl 20 salicylate under conditions conducive to the formation of two liquid phases, separating said phases, and removing the solvent from each phase to produce portions of said oil respectively exhibiting certain of said characteristics to a great- 25 er and to a lesser degree.

14. A process comprising contacting a lubricating oil of Pennsylvania grade with methyl salicylate under conditions conducive to the formation of two liquid phases, separatingsaid 30 phases, and removing solvent from said phases to produce oil portions respectively of lighter and darker color.

15. A process comprising extracting a lubricating oil fraction with methyl salicylate, said 35 original oil fraction being of a character such that `the rainate produced will have a viscosity at 210 F. at least substantially as high as the viscosity at 210 F. of the original oil.

16. A process comprising extracting a lubricat- 40 ing oil residuum of Pennsylvania grade with methyl salicylate to obtain a raffinate having a viscosity at 210 F. at least substantially as high as the viscosity'at the same temperature of the original oil. 45

17. A process comprising contacting a lubricating oil residuum of Pennsylvania grade with methyl salicylate under conditions conducive to the formation of two phases, and separating said phases to produce oil portions of different char- 50 acteristics.

18. A process comprising contacting a relatively heavy lubricating oil with methyl salicylate under conditions causing the formation of two liquid phases, and separating said phases to pro- 55 duce relatively heavy oil portions of higher and lower gravity index, said original oil being of a character such that the raffinate portion will have a viscosity index above 100. 60

WILBERT B. McCLUER. y MERRELL R. FENSKE. 

